JP2022041013A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control system of an internal combustion engine which is advantageous for temperature rise of a catalyst and inhibition of increase in back pressure.SOLUTION: An exhaust emission control system includes a turbine 6T provided in an exhaust passage 4 of an internal combustion engine 1, a bypass passage 12 bypassing the turbine, a catalyst 15 provided in the bypass passage, an adjustment valve 17 for adjusting an exhaust flow rate of the turbine and the catalyst, and a control unit 100 for controlling the adjustment valve. The control unit controls the adjustment valve so that the exhaust flow rate of the catalyst is larger when a load of the internal combustion engine is lower than when the load of the internal combustion engine is high.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust purification system for an internal combustion engine.

A turbocharged turbine is installed in the exhaust passage of the turbocharged internal combustion engine. Further, in the exhaust passage, a catalyst for purifying harmful components in the exhaust is provided on the downstream side of the turbine.

International Publication No. 2010/116541

If the turbine and the catalyst are provided in series in this way, the thermal energy of the exhaust gas is taken away by the turbine, which is disadvantageous for raising the temperature of the catalyst. Further, since the catalyst becomes an exhaust resistance, the exhaust pressure on the upstream side of the catalyst, that is, the back pressure increases, and the efficiency of the internal combustion engine decreases.

Therefore, the present disclosure was devised in view of such circumstances, and an object thereof is to provide an exhaust gas purification system for an internal combustion engine which is advantageous for raising the temperature of a catalyst and suppressing an increase in back pressure.

According to one aspect of the present disclosure.
A turbine installed in the exhaust passage of an internal combustion engine and
A bypass passage that bypasses the turbine and
The catalyst provided in the bypass passage and
A control valve for adjusting the exhaust flow rate of the turbine and the catalyst, and
A control unit configured to control the control valve and
Equipped with
The control unit is provided by an exhaust gas purification system for an internal combustion engine, characterized in that when the load of the internal combustion engine is low, the control valve is controlled so that the exhaust flow rate of the catalyst is larger than when the load is high. Will be done.

Preferably, the control valve is formed by a three-way solenoid valve provided at a branch point of the bypass passage.

Preferably, the exhaust purification system branches from the exhaust passage located downstream of the turbine and upstream of the confluence of the bypass passage, downstream of the branch point of the bypass passage and upstream of the catalyst. Further provided with a branch passage that joins the bypass passage located on the side,
The control valve is formed by a three-way solenoid valve provided at a branch point of the bypass passage and a three-way solenoid valve provided at the branch point of the branch passage.

Preferably, the catalyst is a selective reduction NOx catalyst.
The exhaust purification system includes a urea water injection valve provided in the bypass passage located on the upstream side of the catalyst, and an acquisition unit for acquiring the temperature of the catalyst.
The control unit discharges urea water from the urea water injection valve when the exhaust flow rate of the catalyst is greater than a predetermined value and the temperature of the catalyst acquired by the acquisition unit is equal to or higher than a predetermined activity start temperature. Inject.

Preferably, the exhaust purification system is provided in the exhaust passage located downstream from the confluence of the bypass passage, and further includes a downstream catalyst of the same type as the catalyst.

Preferably, the catalyst and the downstream catalyst are selective reduction NOx catalysts.

According to the present disclosure, it is possible to provide an exhaust gas purification system for an internal combustion engine, which is advantageous for raising the temperature of a catalyst and suppressing an increase in back pressure.

It is a schematic diagram which shows the exhaust gas purification system of 1st Embodiment. A map for calculating the valve opening target value is shown. It is a graph which shows the relationship between an engine load and a valve opening target value. It is a flowchart of a control routine. The map of the first modification for calculating the valve opening target value is shown. The map of the 2nd modification for calculating the valve opening target value is shown. It is a schematic diagram which shows the exhaust gas purification system of 2nd Embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

[First Embodiment]
FIG. 1 shows an exhaust gas purification system of the first embodiment. The internal combustion engine (engine) 1 to which this system is applied is an in-line 4-cylinder vehicle diesel engine. Vehicles (not shown) are large vehicles such as trucks. However, the type, type, application, etc. of the internal combustion engine are not limited.

The engine 1 includes an engine main body 2 and an intake passage 3 and an exhaust passage 4 connected to the engine main body 2. The engine body 2 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and moving parts such as a piston, a crankshaft, and a valve housed therein. The intake and exhaust flows are indicated by white arrows and black arrows, respectively.

Each cylinder is provided with an injector (not shown) that directly injects fuel into the cylinder 5. The compressor 6C of the turbocharger 6 is provided in the intake passage 3.

The exhaust passage 4 is provided with a turbine 6T of the turbocharger 6, an oxidation catalyst 7, a filter 8, a urea water injection valve 9, a selective reduction NOx catalyst 10, and an ammonia oxidation catalyst 11 in this order from the upstream side.

The oxidation catalyst 7 oxidizes and purifies the unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust, heats and raises the exhaust gas with the reaction heat at this time, and NO in the exhaust. Oxidizes to ₂ . The filter 8 is formed by a so-called continuously regenerating catalytic particulate filter, collects particulate matter (PM (Particulate Matter)) contained in the exhaust gas, and continuously burns and removes the collected PM. .. The selective reduction type NOx catalyst 10 reduces NOx in the exhaust by using ammonia derived from urea water injected from the urea water injection valve 9 as a reducing agent. The ammonia oxidation catalyst 11 oxidizes and purifies the excess ammonia discharged from the NOx catalyst 10.

The engine 1 is provided with a bypass passage 12 that bypasses the turbine 6T. The bypass passage 12 is branched from the exhaust passage 4 at a branch point 13 located on the upstream side of the turbine 6T, and joins the exhaust passage 4 at a confluence 14 located on the downstream side of the turbine 6T and upstream of the oxidation catalyst 7. ..

Another catalyst is provided in the bypass passage 12. This other catalyst is specifically a selective reduction NOx catalyst 15. Another urea water injection valve 16 is provided in the bypass passage 12 located on the upstream side of the NOx catalyst 15. For the following distinction, the NOx catalyst 15 and the urea water injection valve 16 provided in the bypass passage 12 are referred to as a pre-stage catalyst 15 and the pre-stage injection valve 16, and the NOx catalyst 10 and the urea water injection valve 9 provided in the exhaust passage 4 are referred to as a pre-stage catalyst 15 and a pre-stage injection valve 16. It is referred to as a post-stage catalyst 10 and a post-stage injection valve 9.

As described above, the exhaust passage 4 located on the downstream side of the confluence 14 of the bypass passage 12 is provided with the same type of downstream catalyst as the front catalyst 15, that is, the rear catalyst 10.

Incidentally, exemplifying the relationship between the front-stage catalyst 15 and the rear-stage catalyst 10 in the present embodiment, the rear-stage catalyst 10 is the main catalyst, and the front-stage catalyst 15 is an auxiliary catalyst. Therefore, the capacity of the rear-stage catalyst 10 is larger than that of the front-stage catalyst 15. Exhaust gas is constantly flowed through the subsequent catalyst 10. The pre-stage catalyst 15 is used as an auxiliary in a situation where NOx cannot be sufficiently removed mainly by the post-stage catalyst 10 alone. By adding the pre-stage catalyst 15 in this way, the amount of NOx that can be reduced can be increased, and it becomes possible to respond to the tightening of exhaust gas regulations.

The engine 1 is provided with a control valve for adjusting the exhaust flow rate of the turbine 6T and the pre-stage catalyst 15. The control valve of the present embodiment is formed by a solenoid valve 17 provided at a branch point 13 of the bypass passage 12. The solenoid valve 17 is formed by a three-way solenoid valve. For convenience, this solenoid valve 17 is referred to as a first solenoid valve 17.

The first solenoid valve 17 has a first position A in which the exhaust passage 4 on the upstream side is connected only to the bypass passage 12 (previous stage catalyst 15 side), and the exhaust passage 4 on the upstream side thereof is connected to the exhaust passage 4 on the downstream side (turbine). It is possible to switch to the second position B connected only to the 6T side). The first solenoid valve 17 can be continuously and steplessly switched between the first position A and the second position. The opening degree S of the first solenoid valve 17 is 100% (fully open) when it is in the first position A and 0% (fully closed) when it is in the second position B, and is stepless and continuous from 0% to 100%. Is variable.

Attached to the engine 1, a control unit, a circuit element (circuitry), or an electronic control unit (called an ECU (Electronic Control Unit)) 100 forming a controller is provided. The ECU 100 is configured to control an injector, a rear stage injection valve 9, a front stage injection valve 16, and a first solenoid valve 17.

The ECU 100 has a rotation speed sensor 40 for detecting the rotation speed of the engine (specifically, the number of revolutions per minute (rpm)) and an accelerator opening degree that is correlated with or proportional to the amount of operation of the accelerator pedal of the driver. An accelerator opening sensor 41 for detection is electrically connected. Further, the ECU 100 is electrically connected with an exhaust temperature sensor 42 for detecting the exhaust temperature on the inlet side of the rear-stage catalyst 10 and an exhaust temperature sensor 43 for detecting the exhaust temperature on the inlet side of the front-stage catalyst 15. To.

The ECU 100 injects fuel from the injector according to a predetermined map (may be a function; the same applies hereinafter) based on the engine speed Ne and the accelerator opening Ac detected by the rotation speed sensor 40 and the accelerator opening sensor 41, respectively. The target fuel injection amount Q, which is the target value of the amount, is calculated. The target fuel injection amount Q is a parameter representing the engine load. For this parameter, other parameters such as accelerator opening degree Ac or required torque may be used instead of the target fuel injection amount Q.

Further, the ECU 100 estimates the temperature of the pre-stage catalyst 15 based on the exhaust temperature detected by the exhaust temperature sensor 43. Alternatively, an exhaust temperature sensor may be provided on the outlet side of the pre-stage catalyst 15 and the temperature of the pre-stage catalyst 15 may be estimated based on the detection values of the exhaust temperature sensors on the inlet side and the outlet side. Any method including a known method can be adopted as the estimation method. The ECU 100 may directly detect the temperature of the pre-stage catalyst 15 by a temperature sensor provided on the pre-stage catalyst 15 itself. These estimations and detections are collectively called acquisition. In this embodiment, the acquisition unit is configured by the exhaust temperature sensor 43 and the ECU 100.

Similarly, the ECU 100 estimates the temperature of the post-stage catalyst 10 based on the exhaust temperature detected by the exhaust temperature sensor 42. The same applies to the points that can be estimated including the detection value of the exhaust temperature sensor on the outlet side of the rear-stage catalyst 10 and that the temperature of the rear-stage catalyst 10 can be directly detected.

In the present embodiment, the exhaust temperature sensors 42 and 43 are provided on the downstream side of the subsequent injection valves 9 and 16, respectively, but they may be provided on the upstream side.

Here, as a comparative example different from the present embodiment, the bypass passage 12 and the first solenoid valve 17 are omitted, and the urea water injection valve 16, the exhaust temperature sensor 43, and the front-stage catalyst 15 are located downstream of the turbine 6T and as an oxidation catalyst. It is assumed that an example is provided in the exhaust passage 4 located on the upstream side of 7. In this case, the turbine 6T and the pre-stage catalyst 15 are provided in series with the exhaust passage 4.

In this case, since the thermal energy of the exhaust gas is taken away by the turbine 6T, it is disadvantageous for raising the temperature and activating the pre-stage catalyst 15. Further, since the front-stage catalyst 15 becomes an exhaust resistance, the exhaust pressure, that is, the back pressure on the upstream side of the front-stage catalyst 15 increases, and the efficiency of the internal combustion engine decreases. Incidentally, when the exhaust pressure on the upstream side of the pre-stage catalyst 15 rises, the differential pressure between the inlet side and the outlet side of the turbine 6T decreases, so that the efficiency of the turbine 6T decreases.

Therefore, in the present embodiment, in order to solve this problem, the above configuration is used, and the following control is executed. Briefly, the ECU 100 controls the first solenoid valve 17 so that when the load of the engine is low, the exhaust flow rate of the front-stage catalyst 15 is larger than when the load is high.

Specifically, the ECU 100 calculates the valve opening target value St corresponding to the engine speed Ne and the load L according to a predetermined map (may be a function; the same applies hereinafter) as shown in FIG. 2, and also calculates the first solenoid. The actual opening degree S (%) of the valve 17 is controlled to be equal to the valve opening degree target value St. Specifically, the load L is the target fuel injection amount Q, and the target fuel injection amount Q increases as the load L increases. In this map, FIG. 3 shows the relationship between the engine load L and the valve opening target value St when the engine speed Ne is a constant speed.

In FIG. 3, the vertical axis is the opening degree S (%) of the first solenoid valve 17, 0 (%) is fully closed, and 100 (%) is fully open. When fully closed, the bypass passage 12 is completely closed, and the exhaust flow rate of the front-stage catalyst 15 becomes zero. Therefore, the entire amount of the exhaust gas supplied from the engine body 2 to the branch point 13 is supplied to the turbine 6T, and the exhaust flow rate of the turbine 6T becomes maximum.

As the opening degree S increases, the opening amount of the bypass passage 12 and the exhaust flow rate of the front-stage catalyst 15 increase, and the exhaust flow rate of the turbine 6T decreases. When the opening degree S reaches 100 (%), the opening amount of the bypass passage 12 and the exhaust flow rate of the front-stage catalyst 15 become maximum, and the exhaust flow rate of the turbine 6T becomes zero.

The exhaust gas flow rate supplied to the branch point 13 is F0, the exhaust gas flow rate of the front stage catalyst 15 is F1, the exhaust gas flow rate of the turbine 6T is F2, and R1 = F1 / F0 is the distribution ratio of the exhaust gas flow rate in the front stage catalyst 15, that is, the first distribution ratio. , R2 = F2 / F0 is defined as the distribution ratio of the exhaust gas flow rate in the turbine 6T, that is, the second distribution ratio. In this case, as the opening degree S of the first solenoid valve 17 increases, the first distribution ratio R1 increases and the second distribution ratio R2 decreases.

The horizontal axis of the map is the engine load L. Lmin is the minimum load, which corresponds to the engine load when the accelerator pedal is completely returned and the accelerator opening Ac is the minimum value, that is, 0 (%). The target fuel injection amount Q at this time is equal to the fuel injection amount at idle. Lmax is the maximum load, which corresponds to the engine load when the accelerator pedal is depressed to the maximum and the accelerator opening degree Ac is the maximum value, that is, 100 (%).

The threshold Ls is preset in the intermediate load between the minimum load Lmin and the maximum load Lmax. The valve opening target value St shown by the thick solid line is 100 (%) when L ≦ Ls and 0 (%) when L> Ls.

According to this map, the ECU 100 controls the opening degree S of the first solenoid valve 17 to 100 (%) equal to the valve opening degree target value St when the actual engine load L is a low load equal to or less than the threshold value Ls. .. Further, when the actual engine load L is a high load larger than the threshold value Ls, the opening degree S of the first solenoid valve 17 is controlled to 0 (%) equal to the valve opening degree target value St. The actual engine load L corresponds to the actual target fuel injection amount Q, and the threshold value Ls corresponds to the target fuel injection amount Q corresponding to the threshold value Ls.

Assuming that the opening degree S of the first solenoid valve 17 is 100 (%) when the load is low, the exhaust flow rate of the front-stage catalyst 15 becomes maximum and the exhaust flow rate of the turbine 6T becomes zero, as described above. Therefore, the high-temperature exhaust gas supplied from the engine body 2 can be supplied to the front-stage catalyst 15 to the maximum. Further, since the pre-stage catalyst 15 is provided in the bypass passage 12 in parallel with the turbine 6T, it is not necessary to supply the exhaust gas after the thermal energy is deprived by passing through the turbine to the pre-stage catalyst 15. This is extremely advantageous for raising the temperature and activating the pre-stage catalyst 15. In particular, during idle warm-up after a cold start, the exhaust gas from the engine body 2 can be directly supplied to the pre-stage catalyst 15 without going through the turbine 6T, so that the pre-stage catalyst 15 can be activated at an early stage. Become. When the load is low, there is little need for supercharging by the turbocharger 6, so there is no particular problem even if the exhaust flow rate of the turbine 6T becomes zero.

On the other hand, when the opening degree S of the first solenoid valve 17 is set to 0 (%) at the time of high load, the exhaust flow rate of the turbine 6T becomes maximum and the exhaust flow rate of the front-stage catalyst 15 becomes zero as described above. Therefore, it is possible to supply the entire amount of exhaust gas to the turbine 6T and perform necessary and sufficient supercharging by the turbocharger 6. Further, since it is not necessary to flow the exhaust gas to the front-stage catalyst 15 at this time, it is possible to suppress an increase in back pressure due to the presence of the front-stage catalyst 15, and thus a decrease in engine efficiency. It is also possible to suppress a decrease in turbine efficiency due to an increase in back pressure. Since the exhaust gas after passing through the turbine passes through the rear stage catalyst 10, even if the front stage catalyst 15 is bypassed, the NOx in the exhaust can be purified without any trouble by the rear stage catalyst 10.

As described above, according to the present embodiment, when the engine load is low (L ≦ Ls), the first solenoid valve 17 is provided so that the exhaust flow rate of the pre-stage catalyst 15 is larger than when the engine load is high (L> Ls). Since it is controlled, it is possible to provide an exhaust gas purification system that is advantageous for raising the temperature of the pre-stage catalyst 15 and suppressing the increase in back pressure.

In view of the above viewpoint, it is preferable to set the threshold value Ls of the engine load to a value that optimally balances the emission requirement for improving the activity of the pre-stage catalyst 15 and the engine output requirement due to supercharging. Further, the threshold value Ls may be changed according to the engine speed Ne.

By the way, the post-stage catalyst 10 cannot substantially purify NOx unless its temperature Tc2 becomes equal to or higher than a predetermined activity start temperature Tc2s. Therefore, the ECU 100 operates the post-stage injection valve 9 only when the estimated temperature Tc2 of the post-stage catalyst 10 is equal to or higher than the activity start temperature Tc2s, and stops the post-stage injection valve 9 at other times. As a result, wasteful urea water injection by the post-stage injection valve 9 can be suppressed. The same applies to the combination of the pre-stage catalyst 15 and the pre-stage injection valve 16.

However, even if the temperature Tc1 of the front-stage catalyst 15 is equal to or higher than the predetermined activity start temperature Tc1s, when the exhaust flow rate of the front-stage catalyst 15 is zero, urea water injection by the front-stage injection valve 16 is useless. Therefore, in the present embodiment, in the ECU 100, the exhaust flow rate F1 of the pre-stage catalyst 15 is larger than the predetermined value F1s (specifically, zero), and the estimated temperature Tc1 of the pre-stage catalyst 15 is equal to or higher than the predetermined activity start temperature Tc1. Occasionally, the front-stage injection valve 16 is operated, and at other times, the front-stage injection valve 16 is stopped. As a result, wasteful urea water injection by the front-stage injection valve 16 can be suppressed.

For example, from the first state where the engine load L is higher than the threshold value Ls (the exhaust flow rate F1 of the front stage catalyst 15 is zero) and the temperature Tc1 of the front stage catalyst 15 is less than the activity start temperature Tc1, the engine load L is the threshold value Ls. It is assumed that the second state is changed to a lower state (the exhaust flow rate F1 of the front-stage catalyst 15 is larger than zero). At this time, since the temperature Tc1 of the pre-stage catalyst 15 is still lower than the activity start temperature Tc1 immediately after the change, the urea water injection by the pre-stage injection valve 16 is not executed. However, when a certain time elapses after the change, the temperature Tc1 of the pre-stage catalyst 15 rises to the activity start temperature Tc1 or higher, so that urea water injection by the pre-stage injection valve 16 is executed. In this way, the urea water injection before the activity start temperature Tc1 or higher can be effectively suppressed.

The predetermined value F1s of the exhaust flow rate is not limited to zero, and may be a value slightly larger than zero. This is because when the exhaust flow rate is slightly larger than zero, the amount of NOx contained in the exhaust gas is also small, so that there is no substantial problem even if the urea water injection is stopped.

Next, the control routine in the present embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 every predetermined calculation cycle τ (for example, 10 ms).

First, in step S101, the ECU 100 acquires the values of the actual engine speed Ne and the engine load L.

Next, in step S102, the ECU 100 calculates the valve opening target value St from the map shown in FIG. 2 based on the acquired engine speed Ne and engine load L.

Next, in step S103, the ECU 100 controls the actual opening degree S of the first solenoid valve 17 to an opening degree equal to the valve opening degree target value St.

After that, in step S104, the ECU 100 determines whether or not the valve opening target value St is larger than 0 (%), that is, whether or not the exhaust flow rate F1 of the pre-stage catalyst 15 is larger than the predetermined value F1s, that is, zero.

When the valve opening target value St is larger than 0 (%), that is, when the exhaust flow rate F1 of the pre-stage catalyst 15 is larger than zero, the ECU 100 proceeds to step S105, and is the temperature Tc1 of the pre-stage catalyst 15 equal to or higher than the activity start temperature Tc1s? Judge whether or not.

When the activation start temperature is Tc1s or higher, the ECU 100 proceeds to step S106, activates (ON) the pre-stage injection valve 16, and ends the routine.

On the other hand, when the valve opening target value St is equal to 0 (%) in step S104, that is, when the exhaust flow rate F1 of the pre-stage catalyst 15 is zero, and when the temperature Tc1 of the pre-stage catalyst 15 is less than the activity start temperature Tc1s in step S105. In some cases, the ECU 100 proceeds to step S107, stops (OFF) the pre-stage injection valve 16, and ends the routine.

In the basic control example described here, as shown in FIG. 3, the valve opening target value St is switched to two stages of 100% and 0% with the engine load threshold value Ls as a boundary. However, it is not always necessary to switch between 100% and 0%. A value smaller than 100% (for example, 80%) may be used instead of 100%, and a value larger than 0% (for example, 20%) may be used instead of 0%. However, the former needs to be larger than the latter.

Next, a modification of the control will be described.

(First modification)
In the above-mentioned basic control example, as shown in FIG. 3, the valve opening target value St is simply switched to two stages.

On the other hand, in the first modification described here, as shown in FIG. 5, the method of switching the valve opening target value St is different. That is, in the map shown in FIG. 5, when the engine load L is larger than the threshold value Ls, the valve opening target value St is set to a constant 0 (%) as in the basic control example, but the engine load L is a threshold. When the value is Ls or less, the valve opening target value St is steplessly and continuously increased from 0 (%) to 100 (%) as the engine load L decreases.

Even with this map, when the engine load L is equal to or less than the threshold value Ls, the exhaust flow rate of the pre-stage catalyst 15 can be increased as compared with the case where the engine load L is larger than the threshold value Ls, so that the same effect as in the basic control example can be exhibited. Further, when the engine load L is equal to or less than the threshold value Ls, the higher the engine load L, the smaller the exhaust flow rate of the front-stage catalyst 15, which is more advantageous than the basic control example in suppressing the increase in back pressure.

The control routine in this first modification is the same as that shown in FIG. However, in the first modification, when the engine load L is equal to or less than the threshold value Ls, the higher the engine load L, the smaller the exhaust flow rate of the front-stage catalyst 15, so the front-stage injection valve 16 is operated (ON). ) (Step S106), it is preferable to reduce the urea water injection amount as the engine load L increases.

(Second modification)
In the second modification, as shown in FIG. 6, the way in which the valve opening target value St changes when the engine load L is equal to or less than the threshold value Ls is different from that in the first modification. That is, in the map shown in FIG. 6, when the engine load L is larger than the threshold value Ls, the valve opening target value St is set to a constant 0 (%) as in the basic control example and the first modification example, but the engine When the load L is equal to or less than the threshold value Ls, the valve opening target value St is gradually increased from 0 (%) to 100 (%) as the engine load L decreases. Even in this way, the same effect as that of the first modification can be exhibited. The number of stages is arbitrary, and in this embodiment, there are five stages. The control routine is the same as that of the first modification.

[Second Embodiment]
Next, a second embodiment of the present disclosure will be described. The same parts as those of the first embodiment will be omitted, and the differences from the first embodiment will be mainly described below.

FIG. 7 shows the exhaust gas purification system of the second embodiment. The exhaust purification system further includes a branch passage 20 that branches from the exhaust passage 4 and joins the bypass passage 12.

The branch passage 20 branches from the exhaust passage 4 at the branch position 21 located on the downstream side of the turbine 6T and on the upstream side of the confluence 14 of the bypass passage 12. Further, the branch passage 20 joins the bypass passage 12 at the merging position 22 located on the downstream side of the branch point 13 of the bypass passage 12 and on the upstream side of the pre-stage catalyst 15.

The control valve of the present embodiment is formed by the above-mentioned first solenoid valve 17 and a second solenoid valve 18 which is another solenoid valve. The second solenoid valve 18 is formed by a three-way solenoid valve and is provided at a branch point 21 of the branch passage 20.

The second solenoid valve 18 has a first position A in which the exhaust passage 4 on the upstream side is connected only to the branch passage 20 (front stage catalyst 15 side), and the exhaust passage 4 on the upstream side thereof is connected to the exhaust passage 4 on the downstream side (rear stage). It is possible to switch to the second position B connected only to the catalyst 10 side). The second solenoid valve 18 can be continuously and steplessly switched between the first position A and the second position. The opening degree S of the second solenoid valve 18 is 100% (fully open) when it is in the first position A and 0% (fully closed) when it is in the second position B, and is stepless and continuous from 0% to 100%. Is variable.

The control of the present embodiment is roughly classified into a control when the engine load L is a low load (threshold value Ls or less) and a control when the engine load L is a high load (greater than the threshold value Ls). Then, each control is changed according to the estimated temperature T of the post-stage catalyst 10.

First, control when the load L of the engine is low (threshold value Ls or less) will be described. When the temperature Tc2 of the subsequent catalyst 10 is low, that is, less than the activity start temperature Tc2s, the opening degree S of the first solenoid valve 17 is controlled to 100%, and the opening degree S of the second solenoid valve 18 is controlled to 0%. As described above, when the rear stage catalyst 10 is inactive, the exhaust gas flow rate of the front stage catalyst 15 is maximized and the exhaust gas flow rate of the turbine 6T is set to zero. Therefore, NOx can be purified by making maximum use of the front stage catalyst 15.

On the other hand, when the temperature Tc2 of the rear-stage catalyst 10 is high, that is, the activity start temperature Tc2s or higher, the opening degrees S of the first solenoid valve 17 and the second solenoid valve 18 are such that the exhaust flow rates of the front-stage catalyst 15 and the turbine 6T are equal (overall). It is controlled to be 50% of each). For example, the opening degree S of the first solenoid valve 17 is controlled to 50%, and the opening degree S of the second solenoid valve 18 is controlled to 0%. When the post-stage catalyst 10 is activated in this way, NOx can be purified by the post-stage catalyst 10, so that the exhaust flow rate of the front-stage catalyst 15 is reduced and the exhaust flow rate of the turbine 6T is increased by that amount. As a result, the increase in back pressure can be suppressed, and the combustion efficiency can be improved by using the turbocharger 6.

Next, control when the load L of the engine is high (greater than the threshold value Ls) will be described. When the temperature Tc2 of the subsequent catalyst 10 is less than the activity start temperature Tc2s, the opening degree S of the first solenoid valve 17 is controlled to 0%, and the opening degree S of the second solenoid valve 18 is, for example, within the range of 0 to 50%. It is variably controlled.

In this case, the exhaust gas supplied from the engine main body 2 is completely supplied to the turbine 6T without branching to the bypass passage 12. A part of the exhaust gas after passing through the turbine 6T is supplied to the front-stage catalyst 15 through the branch passage 20, and the rest is supplied to the rear-stage catalyst 10.

In this case, the engine load L is a high load and a high output torque is required. Therefore, the entire amount of exhaust gas is supplied to the turbine 6T, and supercharging by the turbocharger 6 is executed to the maximum. Then, a part of the exhaust gas is supplied to the pre-stage catalyst 15, and NOx is purified by the pre-stage catalyst 15. At this time, if a large amount of exhaust gas is supplied to the front-stage catalyst 15, the back pressure increases, so that the opening degree of the second solenoid valve 18 is limited to a value less than 100%, for example, in the range of 0 to 50%. By doing so, the increase in back pressure can be suppressed and the engine efficiency can be maximized.

The opening degree S of the second solenoid valve 18 is reduced as the engine load L increases. As a result, as the engine load L increases, the exhaust flow rate of the front-stage catalyst 15 can be reduced and the increase in back pressure can be suppressed.

On the other hand, when the temperature Tc2 of the post-stage catalyst 10 is equal to or higher than the activity start temperature Tc2s, the opening degree S of the first solenoid valve 17 is controlled to 0%, and the opening degree S of the second solenoid valve 18 is also controlled to 0%.

As a result, the exhaust gas supplied from the engine body 2 is completely supplied to the turbine 6T and then supplied to the post-stage catalyst 10. Since the exhaust flow rate of the front-stage catalyst 15 becomes zero, the increase in back pressure can be suppressed to the maximum and the engine efficiency can be maximized.

The control routine is the same as that of the first embodiment, and in step S103 described above, the opening degrees S of the first solenoid valve 17 and the second solenoid valve 18 are controlled as in the present embodiment.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and variations of the present disclosure can be considered.

(1) For example, the front-stage catalyst 15 and the rear-stage catalyst 10 do not have to be selective reduction NOx catalysts. For example, it may be an occlusion-reduced NOx catalyst, or a catalyst other than the NOx catalyst, for example, an oxidation catalyst or a three-way catalyst. The catalyst includes a particulate filter on which a catalyst is supported, such as the filter 8. The type of catalyst may be different between the first-stage catalyst 15 and the second-stage catalyst 10.

(2) If necessary, the post-stage catalyst 10 may be omitted.

(3) The configuration of the control valve can be changed in various ways. For example, two two-way solenoid valves may be provided instead of one three-way solenoid valve to realize the same function.

The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the scope of claims are included in the present disclosure. Therefore, this disclosure should not be construed in a limited way and may be applied to any other technique that falls within the scope of the ideas of this disclosure.

4 Exhaust passage 6T Turbine 10 NOx catalyst (post-stage catalyst)
12 Bypass passage 13 Branch point 14 Confluence point 15 NOx catalyst (pre-stage catalyst)
16 Urea water injection valve (pre-stage injection valve)
17 1st solenoid valve 18 2nd solenoid valve 20 Branch passage 21 Branch point 43 Exhaust temperature sensor 100 Electronic control unit (ECU)

Claims (6)

A turbine installed in the exhaust passage of an internal combustion engine and
A bypass passage that bypasses the turbine and
The catalyst provided in the bypass passage and
A control valve for adjusting the exhaust flow rate of the turbine and the catalyst, and
A control unit configured to control the control valve and
Equipped with
The control unit is an exhaust gas purification system for an internal combustion engine, characterized in that when the load of the internal combustion engine is low, the control valve is controlled so that the exhaust flow rate of the catalyst is larger than when the load is high. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the control valve is formed by a three-way solenoid valve provided at a branch point of the bypass passage. It branches from the exhaust passage located on the downstream side of the turbine and upstream of the confluence of the bypass passage, and joins the bypass passage located on the downstream side of the branch point of the bypass passage and on the upstream side of the catalyst. Further equipped with a branch passage to
The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the control valve is formed by a three-way solenoid valve provided at a branch point of the bypass passage and a three-way solenoid valve provided at the branch point of the branch passage. .. The catalyst is a selective reduction NOx catalyst.
The exhaust purification system includes a urea water injection valve provided in the bypass passage located on the upstream side of the catalyst, and an acquisition unit for acquiring the temperature of the catalyst.
The control unit discharges urea water from the urea water injection valve when the exhaust flow rate of the catalyst is greater than a predetermined value and the temperature of the catalyst acquired by the acquisition unit is equal to or higher than a predetermined activity start temperature. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3. The exhaust purification system for an internal combustion engine according to any one of claims 1 to 4, which is provided in the exhaust passage located on the downstream side of the confluence of the bypass passages and further includes a downstream catalyst of the same type as the catalyst. .. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein the catalyst and the downstream catalyst are selective reduction NOx catalysts.

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